Apparatus for hydrocarbon conversion



J 27, 1953 .1. A; CROWLEY, JR

APPARATUS FOR HYDROCARBON CONVERSION m 9 2 .d m M a I 1 R a a R N M N RE M 0 m. E R 46 Y E V mw u w R N MM mm mm M w 1 EH NY 46 C E d w ,H A 7 z v 9 w n H HHIII 11.5. FLU/0 f MEFLU/D Patented Jan. 27, 1953 APPARATUS FOR HYDROCARBON CONVERSION John A. Crowley, Jr., New York, N. Y., assignor to Socony-Vacuum Oil Company, Incorporated, a corporation of New York Original application February 18, 1947, Serial No.

729,249, now Patent No. 2,571,342, dated October 16, 1951.

Divided and this application October 8, 1947, Serial No. 778,659

4 Claims.

This invention pertains to an apparatus for conversion of high boiling hydrocarbons to lower boiling hydrocarbon products containing substantial amounts of material boiling within the range of aviation and motor gasoline. This invention is particularly concerned with an improved apparatus adapted for hydrocarbon conversion processes in which two separate moving streams of particle form contact material are involved.

It is well known that high boiling hydrocarbons such as gas-oil, for example, when contacted in the vapor phase with a suitable solid adsorbent material at temperatures of the order of 800 F. and usually at pressures above atmospheric, may be converted to lower boiling gaseous, gasoline containing products. Until recently, most commercial catalytic hydrocarbon cracking processes have involved the use of selected cracking stock which consist of material which may be vaporized without undergoing substantial pyrolytic conversion prior to being contacted with the solid catalyst. Recently certain catalytic processes for handling heavier liquid charging stocks have been developed in which the heavy liquid petroleum charged is mixed with a hot catalyst coming from a catalyst regenerator so as to effect vaporization of the liquid oil after which the mixed catalyst and oil vapors are passed through a conversion zone to effect final conversion of the vaporized hydrocarbons to gasoline containing products. In such processes the heat for vaporization of the liquid hydrocarbons and the heat of conversion thereof is all supplied by the hot regenerated catalyst initially contacted with the liquid oil.

This means that the hydrocarbon charge is initially contacted with a very active catalyst at temperatures far in excess of the desired cracking conversion temperature at a relatively high catalyst to oil ratio, resulting in excessive dry gas and coke yields and inferior gasoline yields. Moreover, the total range of catalyst temperatures from the beginning to the end of its contact with the hydrocarbons is undesirably wide.

It has been the practice in thermal cracking operations to subject the very high boiling charging stocks to a preliminary thermal viscositybreaking step to lower the boiling range of the hydrocarbons and to prepare a suitable charging stock for thermal cracking operations. It has also been the custom to subject such high boiilng charging stocks to a thermal coking operation whereby the high boiling liquid residuum is decomposed to yield a substantial amount of coke and non-ccndensible gas as well as a vaporized hydrocarbon fraction suitable for thermal cracking operations. It has recently been suggested that such a coking operation may be accomplished by bringing the liquid petroleum residuum into contact with a mass of inert refractory particles which have previously been heated so as to contain sufficient sensible heat to support the coking reactions. This invention is concerned with an improved apparatus for conducting such coking operations followed by catalytic conversion. This invention also deals with an improved system for conducting such coking operations which avoids the excessive initial coking temperatures characteristic of prior systems. i

A major object of this invention is the provision of an improved apparatus for catalytic conversion of high boiling hydrocarbons.

A specific object of this invention is the provision of an improved apparatus adapted for conversion of hydrocarbons in the presence of two separate moving streams of solid contact material.

Another specific object is the provision of an improved integral petroleum residuum viscositybreaking and catalytic cracking apparatus.

These and other objects of this invention will become apparent from the following discussion of the invention.

In my application Serial Number 729,249, filed in the United States Patent Ofiice February 18, 1947, now Patent No. 2,571,342, I disclose and claim a novel process for vaporizing and cracking high boiling petroleum fractions. In that process a suitable liquid hydrocarbon charge is brought into contact with a substantially compact column of downwardly moving hot heat absorptive material in a confined partial conversion or vaporizing zone in which it is transformed either by conversion to lower boiling hydrocarbons or in some instances merely vaporized to provide a vaporized hydrocarbon fraction suitable for a catalytic conversion operation. Heat absorptive material consists of capsules containing a substance capable of giving up heat (usually by solidification) over a narrow range of temperatures which are suitable for eiiecting the desired partial conversion Or vaporization of the liquid hydrocarbon charge. Used heat absorptive material is withdrawn from the partial conversion or vaporizing zone and heated heat absorptive material is supplied thereto at a rate sufficient to supply the heat required for the transformation of the liquid hydrocarbon charge to said vaporized fraction. The used heat absorptive material is then heated in a separate heating zone usually by direct contact with a suitable heating gas which may, for example, be a flue gas or a heat exchange gas containing sensible heat from the regeneration zone of the catalytic conversion process. The heated heat absorptive material having absorbed a substantial amount of latent heat is then returned to the partial conversion or vaporizing zone as the supply thereto. The resulting vaporized hydrocarbon fraction is passed to a catalytic conversion zone wherein it is contacted with a suitable finely divided adsorbent catalyst wherein to effect the desired conversion, for example, a cracking conversion to gaseous, gasoline containing products. The used catalyst is passed through a suitable regeneration zone wherein the contaminant de posit thereon is removed by burning and is then returned to the conversion zone. The actual catalytic conversion reaction involved in the conversion zone may be a vapor phase hydrocarbon cracking reaction or any of a number of other reactions, for example, catalytic hydrogenation, dehydrogenation, polymerization, isoforming, alkylation, reforming, aromatization, partial oxidation, desulfurizing, etc., of the vaporized hydrocarbon charge.

The contact material employed may partake of the nature of natural or treated clays, bauxites, or synthetic associations of silca, alumina, or silica and alumina. Also the catalyst may take the form of mixtures of metallic oxides, particularly of those from the III and VI groups of the periodic system to which mixture oxides of silica may be added. Other catalysts may consist of carriers such as alumina, carborundum, etc., upon which promoters, usually consisting of certain metallic oxides have been deposited. The exact nature of the catalyst employed will vary depending upon the particular hydrocarbon reactants involved and upon the type of conversion to be accomplished. The size of the catalyst particles will vary depending upon the type process involved. For suspension type processes the catalyst will be in the form of a powder of about 100 mesh and finer as determined by Tyler standard screen analysis. For the moving bed type process the contact material may consist of particles ranging from below 4 mesh to about 60 mesh and preferably from about 4 to 16 mesh.

The size and shape of the capsules of heat absorbent material used in this invention, it will be understood of course, are matters capable of considerable variation without departing from the spirit of this invention. In general it has been found that capsules having an average diameter within the range of about 2 to 8 mm. are satisfactory, but it is not intended that this invention be limited to capsules within that size range or to capsules that are spherical in shape. The heat absorbing substance within the capsules should be one capable of releasing a substantial amount of heat over a narrow range of temperatures which are at a level suitable for the partial conversion or vaporization of the liquid hydrocarbon charge without excessive conversion thereof to gas and coke and above the condensation temperature of the resulting vaporized hydrocarbon fraction. It will be apparent that the material within the capsules should be chosen with reference to the particular liquid hydrocarbon charged and the most suitable temperature for its transformation to the desired vaporized hydrocarbon fraction. Typical substances for use in such capsules and a typical capsule which may be employed in the process of this invention are described in my United States Patent 2,244,- 612 issued June 3, 1941. Preferably the material employed Within the capsules should be a fusible material such as a metal, alloy or inorganic salt or mixtures thereof, having a melting point broadly within the range about 750 F. to 1100 F. and preferably within the range 800 F. to 1000 F. Typical of such substances are the following:

These materials absorb a substantial amount of latent heat of fusion upon being melted and liberate that heat upon solidifying. For example the heat of fusion by calculation of some of the materials listed above is as follows:

70% Mg+30% A1, heat of fusion 76.6 cal/gm; 72% Mg+28% Ni, heat of fusion 72.3 cal./gm.; 23% Cu+7'7% Sb, heat of fusion 39.6 cal/gm.

The present invention in its preferred form involves an integral system for conducting the above described process. However, the present invention in its broader aspects involves a system in which the heat obsorptive material may be other than the capsules above described, for example, fused alumina, quartz, carborundum, and other refractory materials. Moreover, the apparatus is particularly suitable for processes involving lower boiling liquid hydrocarbon charges, which may be vaporized at the desired conversion temperature without serious thermal cracking thereof, for example, gas oils boiling up to about 800 F. and naphtha fractions. Ordinarily these fractions are vaporized in an external tubular heater before being charged to the catalytic conversion vessel. Such a procedure involves the consumption of a considerable amount of heating fuel from a source outside of the catalytic cracking system. The present apparatus eliminates the necessity for external oil charge heaters and transfer lines.

This invention may be most readily understood by reference to the drawings attached hereto of which Figure 1 is an elevational view, partially in section showing the system of this invention and Figure 2 is an enlarged view of one of the capsules of heat absorptive material used in the preferred form of this invention. All of these drawings are highly diagrammatic in form.

Turning now to Figure 1, there is shown an elongated, vertical vessel 10 closed on either end. A partition ll of downwardly tapered construction is provided across the vessel 70 at an intermediate level along its length so as to divide it into an upper vaporizing chamber 72 and a lower conversion chamber 13. Heat absorptive material from hopper I3 is supplied to the upper end of vessel 70 via conduit I 4, and passes into seal chamber 76, defined by means of partition 77 in the upper end of vessel Ill. An iner seal gas is introduced into chamber It via conduit :18. Heat absorptive material passes via tubes 19 depending from partition 11 into the vaporizing chamber I2. The heat absorptive material passes downwardly through chamber I2 as a substantially compact column and is withdrawn from the bottom of vaporizing chamber 12 via conduit 80 which connects into the downwardly tapered partition II. A horizontal partition 8| extends across the lower section of the vaporizing chamber to define at its lower end a seal and purging chamber 82. The heat absorptive material passes thro g he pa tition 8: thr ug uniformly distri t d tubes B3 dependin th re om and is pur ed substantially fre of gase hyd artons in chamber 88. be re dischar ng h ough conduit Bil, by a suitable inert pur e gas such as am int oduc d fr m m nifold 85 t p forated pipes 86 which extend across chamber 82 and issuing from the pipes 85 into the mass of heat absorptive material in chamber 82. Hot particle form catalyst from hopper 39 is passed downwardly through gravity feed leg 45 into the seal chamber 83. The catalyst passes by gravity from a bed thereof in chamber 88 via conduit 9!} into the upper section of chamber It. An inert seal gas is introduced into chamber 83 via conduit 89 at a sufficient rate to maintain a seal gas pressure therein slightly higher than the gaseous pressure in the upper section of chamber I3. A stuffing box 9| is provided at the location of entry of conduit 96 into the side of vessel It! to prevent escape of gas from chamber I3. The catalyst moves downwardly through chamber I3 as a substantially compact column being withdrawn at the lower end of vessel 10 through conduit 92 at the desired rate controlled by valve 83. In order to insure uniform withdrawal of catalyst from all portions of the horizontal cross-sectional area of the conversion chamber 13 suitable bailling should be provided just above the control discharge conduit 92. In the modification shown the baffling takes the form of two vertically spaced horizontal partitions 95 and 95 having orifices 91 and 98 therein. The orifices 91 in the upper partition 95 are uniformly distributed across the partition. The orifices 98 in partition 95 are less in number than the orifices 9i and are horizontally staggered with respect to orifices 9? so that each orifice 98 receives proportionate catalyst flow from a plurality of orifices ill. The streams from orifices 98 are then proportionately merged into the single outlet stream in conduit 92. conduit 95 to manifold ltd from which it passes through pipes Isl under a plurality of horizontally spaced gable-roofed inverted distributing troughs :92 positioned in the lower section of chamber 13. Thus the gaseous hydrocarbon products are substantially purged from the cutflowing spent catalyst. A suitable liquid hydrocarbon charge, for example, a gas oil fraction boiling within the range about 450 F.-75G F. is introduced from manifold m5 int-o headers its which extend across the space III! above the column of heat absorptive material in chamber 52. The liquid oil is then sprayed through nozzles I538 onto the column of heat absorptive material and is vaporized by the heat released in solidifying the substance within the capsules. For example, the substance within the capsules may be a fusible alloy consisting of 70% Bi and Sb, melting at about 878 F. The oil charge is vaporized and he ted o a temperature shortly bel w 878 An inert purge gas is introduced through F. by the time it reaches the lower section of chamber I2. The vaporized oil then passes into the conversion chamber I3 through tubes III], which are connected tightly through partition II and which slide upwardly through partition SI. Inverted conical shaped baffles III are supported by suitable means (not shown) above the tubes Ill! so as to provide disengaging surfaces for disengagement of the vaporized hydrocarbons from the column of heat absorptive material and so as to prevent the gravity flow of heat absorptive capsules into the upper ends of tubes H9. The vaporized hydrocarbon charge passes downwardly through the column of catalyst in hamber 13' to becom converted to gasoline cont in ns products- Thes as s products ar collected under one or more vertical rows f horizontally spaced inverted collectin trou hs H2 within the lower section of chamber 13. The gaseous products are withdrawn from troughs I I; throu h pipe I I 3 to manifo d I It from. whi h they are in turn withdrawn through outlet conduit H5. The spent catalyst from chamber .13 is transferred via conveyor H16 to regenerator H1. The regenerator shown is of the multistage type, consisting of a plurality of burning stages I I8-I 2!! inclusive and a plurality of cooling stages I 2 I-I23 inclusive which alternate in vertical series with the burning stages. Air is supplied from manifold I24 to each of the burning stages through separate inlets I25-I2'I inclusive. Flue gas is withdrawn from the burning stages through separate outlets IZE-IBU inclusive to manifold I3I. If desired, heat transfer tubes or coils may be provided in the cooling stages IZI-IZS inclusive. Heat exchange fiuid may be supplied from manifold I32 to each of these cooling coils through inlet pipes I33 and withdrawn from these cooling coils through pipes I34 to an outlet manifold I 35. In some instances it is desirable to eliminate the heat transfer tubes and to pass a suitable substantially oxygen free cooling gas directly through the catalyst bed in each cooling stage to accomplish heat removal from the catalyst. In such instances the manifold I32 and pipes I33 may serve as inlets for said cooling gas and the pipes I 34 and manifolds I 35 may serve as withdrawal means for the heated gas. The regenerated catalyst is withdrawn from the bottom of the regenerator II'I through conduit I38 at a suitable rate controlled by valve I39. The regenerated catalyst is transferred by conveyor MI to duct I42 supplying the hopper 33. The used heat absorptive material passes by gravity via discharge conduit 80 to the reconditioner M3. It moves downwardly through the reconditioner M3 being withdrawn from the bottom thereof through conduit I44. Hot flue gas from the burning stages of the regenerator existing at a temperature of the order of 950 F.-1 150 F. is directed from manifold I 3i through duct I45 into the lower section of reconditioner M3. The hot flue gas passes upwardly through the column of heat absorptive material so as to supply heat for melting the fusible alloy in the capsules of heat absorptive material. If sufiicient heat is not available from the regenerator flue gas, additional heat may be obtained or all the required heat may be obtained by directing the hot heat exchange gas from cooling stages I2I to I23 inclusive from manifold I35 into duct I and thence into reconditioner I43. The relative amount of gas withdrawn from manifolds I'3I and I35 may be regulated by means of valves I41 and M3 respect vely thereon.- The cooled gases may be withdrawn from the upper section of reconditioner I43 through conduit I49. In the instant example, these efiluent gases may exist at a temperature of the order of 875 F.-885 F. The heated heat absorptive material passes from vessel I43 through conduit 144 to conveyor I50 by which it is returned to hopper I3.

The arrangement shown in Figure 1 may be employed also for the conversion of liquid petroleum residuums in which event the chamber I2 serves as a partial conversion or viscositybreaking zone. Any carbonaceous material deposited upon the capsules may be burned off by means of air introduced to reconditioner I43 at I51. In some instances where the amount of heat recoverable from the regeneration zone is insufiicient for vaporizing or partially converting the liquid petroleum charge, additional heat may be supplied to the system by introduction of a suitable fuel gas into the vessel I43 through conduit I52 to be burned in contact with the heat absorptive material by air introduced into vessel I43 at I5I.

Preferably the heat absorptive material employed may take the form of capsules containing a fusible substance as described hereinabove. A typical form of the heat absorptive bodies is shown in Figure 2, wherein we find the heat absorptive body I60 to be composed of a suitable metal shell within which there is enclosed a suitable substance I62 as described capable of absorbing a substantial amount of heat at a substantially constant temperature level. It will be apparent that when such heat absorptive bodies are employed the heat absorptive material may enter the chamber I2 and discharge therefrom at substantially the same temperature which may be of the order of 950 F., for example. Substantially the total heat for the transformation of liquid hydrocarbon charge to the vaporized fraction is supplied by the release of latent heat by the fusible substance within the capsules. In this manner, excessive conversion temperatures within the chamber I2 are entirely avoided.

It will be understood that this invention is not intended to be limited to the particular details of apparatus design and arrangement hereinabove described. For example, other types of catalyst regenerators adapted to accomplish removal of the carbonaceou contaminant by burning at controlled temperatures may be substituted for the preferred forms which are shown. Also methods for introducing and withdrawing solid material into and from the various vessels other than those shown may be employed. Moreover, other constructions for distributing gases into the several vessels and for removing gases therefrom may be employed. It is also not intended that the invention be limited to the particular details of operating conditions and process applications specifically described hereinabove or otherwise limited except as limited in the following claims.

This application is a division of application Serial Number 729,249, filed in the United States Patent Oifice February 18, 1947, and issued as U. S. Patent No. 2,571,342 on October 16, 1951.

I claim:

1. An apparatus for efiecting conversion of high boiling liquid hydrocarbons to lower boiling gaseous hydrocarbons which comprises: a substantially vertical, elongated vessel, a partition extending across said vessel at an intermediate level along its length dividing said vessel into an upper vaporizing chamber and a lower final conversion chamber, means to introduce solid heat absorptive material particles into the upper section of said upper chamber, means to withdraw said solid material from the lower sec; tion of said upper chamber to a point outside of said vessel, means to introduce a particle-form catalyst into the upper section of said lower chamber, means to withdraw used catalyst from the lower section of said lower chamber, a liquid feed nozzle in the upper section of said upper chamber, piping extending into said upper chain her from the outside and connected to said feed nozzle for supplying liquid feed thereto, means defining a passage for gas flow from the lower section of said upper chamber through said partition to the upper section of said lower chamber, baffle means within said upper chamber adapted to prevent flow of solid material through said passage defining means, and means to withdraw gas from the lower section of said lower chamber.

2. Apparatus for efiecting conversion of high boiling liquid hydrocarbons to lower boiling gaseous hydrocarbons which comprises: a substantially vertical, elongated vessel, a partition extending across said vessel at an intermediate level along its length dividing said vessel into an upper vaporizing chamber and a lower final conversion chamber, means to introduce solid heat absorptive material particles into the upper section of said upper chamber, means to withdraw said solid material from the lower section of said upper chamber to a point outside of said vessel, means to introduce a particle-form catalyst into the upper section of said lower chamber, means to withdraw used catalyst from the lower section of said lower chamber, at least one liquid feed nozzle within the upper section of said upper chamber, piping extending into said upper chamher from outside thereof and connecting to said liquid feed nozzle for supply of liquid feed thereto, means defining a passage for gas flow from the lower section of said upper chamber through said partition to the upper section of said lower chamber, bafile means within said upper chamber adapted to prevent fiow of solid material through said passage defining means, members defining a gas collection space from which gravity flow of solid particles is excluded, within the lower section of said lower chamber, which space communicates along its bottom with the interior of said lower chamber, outlet piping connected into said lower chamber and communicating with the space defined by said members, a separate catalyst regeneration vessel, means to pass used catalyst from said lower chamber to said regeneration vessel, means to contact said catalyst with oxygen containing gas in said regeneration vessel, means to return the regenerated catalyst to the upper section'of said lower chamber, a separate heating vessel, means to pass heat absorptive material from said upper chamber to said heating vessel, means to pass a suitable heating gas through said. heating vessel to contact said heat absorptive material, and means to return heated heat absorptive material from said heating vessel to the upper section of said upper chamber.

3. Apparatus for conversion of high boiling liquid hydrocarbons to lower boiling gasoline containing hydrocarbons which comprises: a substantially vertical elongated vessel, partitioning across said vessel dividing it into an upper vaporizing chamber and a lower conversion chamber, inlet conduit means extending downwardly into the upper section O Said, vessel for gravity flow of solid heat absorptive material thereinto, outlet conduit means, extending downwardly from said partitioning for gravity flow of said heat absorptive material to a point outside of said vessel, inlet conduit means for gravity flow of solid catalyst extending downwardly into the upper section of said lower chamber, outlet conduit means extending downwardly from the lower end of said vessel for withdrawal of catalyst, downwardly facing liquid spray nozzles supported within the upper section of said upper chamber, piping extending into said upper chamber connected to said spray nozzles for supply of liquid hydrocarbon charge thereto, tubes, open on either end extending through said partitioning for fiow of vaporized hydorcarbons from said upper chamber to said lower chamber, baffling over each of said tubes adapted to substantially exclude solid flow from the inlet to said tubes, and a downwardly opening gas collector within the lower section of said lower chamber and passage defining means for withdrawal of gaseous products from under said gas collector.

4. Apparatus for conversion of high boiling liquid hydrocarbons to lower boiling gasoline con taining hydrocarbons which comprises: a substantially vertical elongated vessel, partitioning across said vessel dividing it into an upper vaporizing chamber and a lower conversion chamber, inlet conduit means extending downwardly into the upper section of said vessel for gravity flow of solid heat absorptive material thereinto, outlet conduit means, extending downwardly from said partitioning for gravity flow of said heat absorptive material to a point outside of said vessel, a separate heating vessel, conduit means connecting said outlet conduit means into the upper section of said heating vessel, a heating gas inlet to said heating vessel and a heating gas outlet therefrom, outlet conduit means for heat absorptive material discharge from the lower section of said heating vessel, means to transfer the discharged heated heat absorptive material to said inlet conduit means to said upper vaporizing chamber, inlet conduit means for gravity flow of solid catalyst extending downwardly into the upper section of said lower chamber, outlet conduit means extending downwardly from the lower end of said vessel for withdrawal of catalyst, a separate regeneration vessel, means to transfer catalyst withdrawn from said lower chamber into the upper section of said regeneration vessel, a regeneration gas inlet to said regeneration vessel and a regeneration gas outlet therefrom, outlet conduit means for regenerated catalyst discharge from the lower section of said regeneration vessel, means to transfer the regenerated catalyst to said inlet conduit means to said lower chamber, at least one liquid spray nozzle supported within said upper partial conversion chamber a substantial distance above its lower end but below its upper end, piping extending into said upper chamber connected to said spray nozzle for supply of liquid hydrocarbon charge thereto, uniformly distributed tubes, open on both ends, extending through said partitioning in said first named vessel for gas flow between said upper and lower chambers, bafiles over said tubes adapted to prevent solid heat absorptive material from flowing by gravity thereinto, and means to withdraw gaseous products from said lower chamber.

JOHN A. CROWLEY, JR.

REFERENCES CITED UNITED STATES PATENTS Name Date Crowley Apr. 5, 1949 Number 

1. AN APPARATUS FOR EFFECTING CONVERSION OF HIGH BOILING LIQUID HYDROCARBONS TO LOWER BOILING GASEOUS HYDROCARBONS WHICH COMPRISES: A SUBSTANTIALLY VERTICAL, ELONGATED VESSEL, A PARTITION EXTENDING ACROSS SAID VESSEL AT AN INTERMEDIATE LEVEL ALONG ITS LENGTH DIVIDING SAID VESSEL INTO AN UPPER VAPORIZING CHAMBER AND A LOWER FINAL CONVERSION CHAMBER, MEANS TO INTRODUCE SOLID HEAT ABSORPTIVE MATERIAL PARTICLES INTO THE UPPER SECTION OF SAID UPPER CHAMBER, MEANS TO WITHDRAW SAID SOLID MATERIAL FROM THE LOWER SECTION OF SAID UPPER CHAMBER TO A POINT OUTSIDE OF SAID VESSEL, MEANS TO INTRODUCE A PARTICLE-FORM CATALYST INTO THE UPPER SECTION OF SAID LOWER CHAMBER, MEANS TO WITHDRAW USED CATALYST FROM THE LOWER SECTION OF SAID LOWER CHAMBER, A LIQUID FEED NOZZLE IN THE UPPER SECTION OF SAID UPPER CHAMBER, PIPING EXTENDING INTO SAID UPPER CHAMBER FROM THE OUTSIDE AND CONNECTED TO SAID FEED NOZZLE FOR SUPPLYING LIQUID FEED THERETO, MEANS DEFINING A PASSAGE FOR GAS FLOW FROM THE LOWER SECTION OF SAID UPPER CHAMBER THROUGH SAID PARTITION TO THE UPPER SECTION OF SAID LOWER CHAMBER, BAFFLE MEANS WITHIN SAID UPPER CHAMBER ADAPTED TO PREVENT FLOW OF SOLID MATERIAL THROUGH SAID PASSAGE DEFINING MEANS, AND MEANS TO WITHDRAW GAS FROM THE LOWER SECTION OF SAID LOWER CHAMBER. 